The goal of this proposed study is to improve the efficacy of body weight supported treadmill training (BWSTT) in children with cerebral palsy (CP) using a novel robotic therapy that applies controlled forces to the leg during the swing phase of gait. CP is the most prevalent physical disability originating in childhood with an incidence of 2-3 per 1,000 live births. Reduced waking speed and endurance are two of the main functional problems. As a consequence, there is a desire to develop new techniques to improve walking function in children with CP. While BWSTT has been used to improve locomotor function in children with CP, it remains unclear whether therapeutic effects of such training are maximized and further evidence is needed to support BWSTT in pediatric practice. In addition, a major limitation of BWSTT is that it requires greater involvement of the physical therapist. Current robot assisted BWSTT demonstrates effectiveness in reducing therapist labor in locomotor training but shows limited functional gains in some patients. Our goal is therefore to improve the efficacy of BWSTT by applying controlled resistance load to the leg during treadmill training. Evidence from animal studies indicates that gait retraining is more effective with assistance as needed than with a fixed trajectory paradigm. Similarly, results from adults post stroke arm study suggested that causing adaptation by using error-augmentation training might be an effective way to promote functional motor recovery. We postulate that providing tolerated resistance load based on the motor performance of the children with CP will improve the training outcomes of BWSTT through enhanced patient effort that effectively engages adaptive sensorimotor processes. Accordingly, our specific aims are: Aim1. Demonstrate motor adaptation to applied loads in children with CP. Specifically, we aim to assess the motor adaptation to controlled resistance load in children with CP. The muscle activities and kinematics of the lower extremities will be recorded to quantify the motor adaptive effects of resistance loads. We expect that leg muscle activity and limb kinematics will adapt to applied loads and show aftereffects when removed. In addition, we will exam the carryover of the motor adaption associated with the resistance training from the treadmill to overground walking. Aim 2. Improve gait in children with CP using a resistance as tolerated strategy. We will assess the locomotor function improvement in children with CP following resistance load training. Specifically, gait speed, endurance, and clinical measurements of motor function will be obtained at pre, post training, and at the follow up. Significant improvements are expected in the BWSTT combined with resistance, compared to the assistance training group. The results from this study will lead to an innovative clinical therapy aimed at improving locomotor function in children with CP. We anticipate that this technique will be useful for improving gait in children with CP through robot-assisted BWSTT.